After antibody testing (rabbit monoclonal), the results revealed GATA3 positivity in tumor cells, ER-positive nuclear expression in over 90% of tumor cells, negative PgR nuclear expression, Human Epidermal Growth Factor Receptor 2 (HER2) negativity with a score of 1 according to the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2018 revised criteria, a Ki-67-positive nuclear proliferation index in approximately 20% of tumor cells, and TTF1 negativity. The gene discussed is ERBB2; the disease is neoplasm.